Rate law from a mechanism
A reaction occurs in two steps. Step 1 (slow): NO2 + NO2 → NO3 + NO. Step 2 (fast): NO3 + CO → NO2 + CO2. What is the rate law?
Answer A: explanation for every choice
A
Correct. The slow step determines the rate, and its molecularity gives the rate law.
B
This comes from the overall equation, which doesn't determine the rate law.
C
This is the fast step, and NO3 is an intermediate that can't appear in the rate law.
D
CO enters only after the rate-determining step.
TakeawayThe rate law comes from the slow step. Intermediates don't appear in it.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp140.